Relationship between age and measures of balance, strength and gait: linear and non-linear analyses.

An age-related decline in balance, gait and lower-extremity muscle strength measures may lead to increased risk of falls and fractures. Previous studies have reported a possible non-linear age-related decline in these measures, but the choice of methodological approach has limited its interpretation. Healthy community-dwelling women (n=212) 21-82 years of age were evaluated for strength [Nicholas MMT (manual muscle tester)], gait [CSA (clinical stride analyser)], activity [HAP (human activity profile)] and static and dynamic balance [CBS (Chattecx balance system), LBT (Lord's balance test) and the ST (step test)]. A GAM (generalized additive model) was developed for each outcome variable to estimate the functional relationship, with age as a continuous variable. Performance was maintained until 45-55 years of age, depending on the outcome measure. Thereafter a decline in performance was evident with increasing age in all measures. Overall, a significant non-linear relationship with age was demonstrated for lower-extremity strength measures (MMT), velocity and double support duration of gait (CSA) and some clinical and laboratory balance tests [ST, LBT (eyes open) and the CBS]. Linear relationships were demonstrated by the LBT with eyes closed and activity measures. Balance, lower-extremity muscle strength and gait may decline non-linearly with age. Our study suggests possible threshold effects between age and balance, muscle strength and gait measures in women. Further research into these threshold effects may have implications for the optimal timing of exercise and other interventions to reduce the risk of falls and fractures.